1. Field of the Invention
This invention relates to an electrochemical bipolar reactor for processing industrial wastes. In particular, this invention relates to a reactor containing conductive particles held in a fixed relationship to one another with non-conductive material wedged between some of the particles.
2. Description of the Prior Art
Bipolar electrochemical reactors are known. One such reactor is described in U.S. Pat. No. 3,900,377. The reactor or cell described in that patent has numerous ported bipolar electrodes or plates contained within the reactor together with primary electrodes. These bipolar electrode plates tend to be fragile, as well as being expensive to manufacture at present. In addition, the reactor must be operated under relatively precise conditions. Although the type of reactor described in U.S. Pat. No. 3,900,377 is suitable and economical for processing small quantities of wastes (e.g. 10-20 tons per day), it is not practical or economical for scaling up to treat wastes at the rate of 100-2,000 tons per day commonly produced in various hydrometallurgical and industrial processes.
There are known bipolar electrochemical reactors having a series of bed sections containing electrically conductive particles. In these reactors, the conductive particles are generally contained in fluidized beds but the beds are separated from one another by insulated spacers. These reactors can suffer from a disadvantage in that they have a relatively high void volume and can occupy a relatively large space because of the distance between adjacent insulating spacers. In addition, these reactors can be expensive because they must be constructed in a very precise manner with an appropriate distance between insulating spacers and each insulating spacer must be independently supported. In addition, when fluidized beds are used to process industrial waste, numerous problems can be encountered. If the particles are not substantially uniform in size, the finer particles can become lodged in the openings in the insulating spacer and thus reduce the flow of electrolyte through the reactor. When graphite particles are used, even if the particles are initially the same size, the particles are frangible and fine particles are produced after a relatively short period of operation. Again, the fine particles can become lodged in the openings in the insulating spacer and reduce the flow of electrolyte through the reactor. The flow rate of fluidized beds is often extremely critical and expensive flow control means are often required. In addition, when gas bubbles are produced during the electrolysis reaction, they tend to adhere to the particles within the fluidized bed. When this occurs, the particles rise to the top of the fluidized bed and can block the flow of electrolyte. If the industrial waste being treated contains plateable metals, as metal becomed plated onto the particles, the density of the particles changes and the flow rate of the fluidized bed must be adjusted. Also, if the industrialized waste being treated contains suspended solids, unless the solids content is very low or the waste is filtered before entering the electrochemical reactor, the waste cannot be processed in a fluidized bed system. Finally, because fluidized beds have a relatively large void volume, the voltage drop is usually much larger than that of a bipolar reactor containing particles with a relatively low void volume. If the voltage drop is higher with fluidized beds, then the cost of processing is higher. A serious problem with all fluidized or semifluidized bed reactors is the high degree of current leak. Current leak is defined as the current which passes through the interstitial solution between the primary electrodes without passing through the conductive particles. The current (energy) leak does not function to make the conductive particles bipoles. The energy is simply dissipated as heat. The percent current leak is inherently high in all partially expanded or fluidized bed reactors. For example, in tests with conductive beds of graphite particles ranging from 0.8 to 1.2 mm, a current leak of about 70% was experienced for a bed expansion of 50%. The current leak increased to about 80% for a bed expansion of 100-120%. Thus, although in theory a fluidized bed bipolar system provides potentially large anodic an cathodic surface area per unit mass of conductive charge and would therefore appear to be the ideal bipolar electrode reactor, problem relating to hydrodynamic, flow control, particle abrasion and current leakage can render such a system impractical for large scale industrial applications.
It is an object of the present invention to provide a discrete particulate bipolar electrochemical reactor that overcomes the problems above and can be easily constructed with readily attainable materials. It is a further object of the present invention to provide a bipolar electrochemical reactor that is rugged, durable and simple to operate.